In recent years, enhancement of high integration, high function, and high dense packaging have been accelerated in semiconductors widely used in electronic apparatuses, communication apparatuses, and personal computers, and demands for properties of laminates for semiconductor plastic packages and high reliability thereof have been increased.
In particular, it has been strongly demanded that a reduction in the coefficient of thermal expansion in the planar direction of the laminate for semiconductor plastic packages and an enhancement in the resistance against chemicals of the laminate be satisfied at the same time.
Such a demand for the reduction in the coefficient of thermal expansion in the planar direction of the laminate comes from the following reason. When the difference in the coefficient of thermal expansion between a semiconductor element or a semiconductor plastic package and a laminate such as a printed circuit board for a semiconductor plastic package is large, a thermal impact applied to the laminate causes warpage in the laminate due to this difference in the coefficient of thermal expansion. This warpage causes connection deficits between the semiconductor element or the semiconductor plastic package and the laminate.
To solve such a problem, for example, Patent Literature 1 describes reducing the coefficient of thermal expansion of a cured product (laminate) prepared from a thermosetting resin composition by increasing the content of an inorganic filler. Patent Literature 2 describes use of a silicone rubber as a powder having rubber elasticity and fused silica as an inorganic filler to prepare a resin composition that can attain a laminate having high flame retardancy and low thermal expansion in the planar direction.
The demand for an enhancement in the resistance against chemicals of the laminate comes from the following reason. The process of preparing a laminate such as a printed circuit board includes steps during which the laminate is exposed to a variety of chemical solutions, such as etching, desmearing, and plating. If the laminate has low resistance against chemicals, it leads degradation of the laminate and a reduction in productivity. Specifically, when a laminate has insufficient resistance against chemicals, the plastic layer in the laminate elutes into the chemical solution to contaminate the chemical solution. The laminate is degraded by use of such a contaminated chemical solution.
If the chemical solution is frequently replaced to prevent such a degradation of the laminate, cost increases and the amount of production reduces, leading to a significant reduction in the productivity of the laminate.
In particular, the desmearing step uses a strong alkaline chemical to remove smears generated by mechanical drilling or laser drilling. In the laminate having insufficient resistance against chemicals, inner walls of through holes and the surface of the plastic layer as well as the smears elute to readily contaminate the chemical solution.